Production of aluminum alloy castings, for example massive production of automobile engine parts, is usually made in permanent-type or semi-permanent type molds, in contrast with molds made of sand which are used for only one casting and are destroyed when the casting is extracted therefrom. The permanent or semi-permanent molds are provided with cooling means which accelerate the solidification process of a casting thus raising the productivity of the casting plant. Whenever the molds are taken out of operation, and have to be used again, or the casting system undergoes delays, the temperature in several portions of the mold drops down and may cause premature solidification of the liquid aluminum. This situation may result in a number of castings of poor quality due to uneven casting flow and solidification or the like, producing costly scrap and time loss with consequent expensive labor and product losses. It has been customary to preheat the molds at the beginning of a casting cycle by means of natural gas-air burners which throw a flame directly over the walls of the mold in order to have some higher temperatures in the mold walls. This preheating however is done without any specific control, and is based on the experience of the operators. The current casting practices do not provide any means or method for assuring that the casting to be made in a given mold will be of good quality without defects due to having been cast in a mold with an uneven temperature distribution or simply an overall lower temperature not suitable for a good quality casting. In spite of such grossly-applied preheating of cold molds, it is common in the art of manufacturing aluminum castings that a certain percentage (commonly as much as 2 to 4%) of the production is accepted as scrap production, because at start up the aluminum is cast in an effectively still "cold" mold (thus, functioning eventually to heat the molds to effective operating temperature, but in the interim producing so-called "warm-up" scrap).
The present invention is related to a method and apparatus for preheating the molds so that no scrap due to this problem is produced and its practice results in savings of millions of dollars per year in a given casting plant.